Photosynthetic acclimation to abiotic stress in an acidophilic microalga from Tinto River

Extreme microorganisms have naturally adapted to cope with extreme physicochemical conditions. We evaluated the photosynthetic response of Coccomyxa onubensis (C. onubensis), a microalga isolated from Tinto River, a highly acidic habitat, when exposed to different stressors: salt, Fe (III), irradiance or nitrogen limitation. The results obtained revealed the activation of acclimation mechanisms of the microalga to the imposed abiotic stress factors. In contrast to other non-extremophilic microalgae, C. onubensis responded to Fe (III) or irradiance stress by apparently reducing its functional antenna size, in a manner consistent with maximization of the photosynthetic use of light, resulting in biomass productivity 50% higher than that of control cells. Analysis of chlorophyll fluorescence (JIP parameters) suggested an acclimation of C. onubensis to salt stress as time progresses. Additionally, although the cultivation of C. onubensis under nitrogen limitation significantly affects the photosynthetic performance of the microalga, resulting in a 3-fold increase in non-photochemical quenching (NPQ) compared to control cells, the photosynthetic efficiency values remained within the range reported for healthy and viable cultures, while moderate biomass productivity values of about 0.5 g L^- 1 d^- 1 were also recorded. These acclimation capabilities could be further applied to the biomass production of acidophilic microalgae and its valuable biomolecules under abiotic stress, providing insights into various areas relevant to society, such as animal and human nutrition, health, agriculture, and water treatment.